grammetry, Remote Sensing and Spatial Information Sciences 
. Vol XXXV, Part B4. Istanbul 2004 
  
  
  
International Archives of the Photo 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Texture LOD layer Texture ID Texture Size Texture Data 05 
0 1096 64X64 JPEG2000Byte [] 
Surface | 1 1096 32X32 JPEG2000Byte [] 
texture | 2 1096 16X16 JPEG2000Byte [] 
3 1096 8X8 JPEG2000Byte [] 
0 1262 128X64 JPEG2000Byte [] 
Surface 1 1262 64X32 JPEG2000Byte [] 
texture? 2 1262 32X16 JPEG2000Byte [] 
3 1262 16X8 JPEG2000Byte [] 
  
  
  
  
  
  
  
  
  
  
  
Tablel. The structure of multi 
4.2 Visibility-based city scene visualization 
When the user begins to roam the city scene, a set of 
parameters such as the height of viewpoint, angle of view 
(AOV), pitch and yaw are computed. 
The data cache of nine multi- resolution city blocks is obtained 
from server side. In the area of data cache, there is the original 
viewpoint (point A) and the end of viewpoint (point B) (see 
figure 5). While the viewpoint is moving from point A to point 
B, only several data blocks need obtained from city model data 
at server side, and it has enough time to transfer the data block. 
At same time dynamic city scene 1s created according to the 
Zz 
/ 
FK. 
N 
N 
x 
Point A 
Figure 5. LOD Blocks for Flying Operation 
parameters of viewpoint. 
  
  
  
  
  
  
  
  
  
5. NETWORK MESSAGES DESIGN 
il to implement the requirements of 
ironments. So, the 
te each 
eration 
The message is proved useft 
multi-user's interaction in the virtual city env 
message is designed to achieve multi-users communica 
other and to assure the consistency of multi-user's op 
and virtual scene. 
The message format is defined as follow: 
<FromlD * *TolD * *msgType * *Range* *RequestReply * 
msgContent> 
From the ID of user who sends message to others 
To the ID of user who receives the message from 
message server 
message type 
MsgType 
request reply 
RequestReply 
1 
-resolution LOD texture 
Range the range of message 
MsgContent the content of message 
6. EXPERIMENTS 
With these methods a Web-based distributed virtual city 
system together with the aspects of visualization interface is 
implemented to 3D city visualize. Especially, the user can see 
his avatar and other user’s avatars in the city environments. 
in this system, the system application server is 
Moreover, 
lication server is 
deployed Unix platform and the other app 
deployed at Windows platform. 
world, the user is able to change the 
ing to his/her viewing habits, it 
which 
Similar to real 
visualization process accord 
provide a interactive process during flying through, 
allows user to input information during procedure of 
visualization to construct a free envision space to fly in it. 
Several experimental results are shown as following in figure.6. 
figure 7, figure 8. 
Wie a 
RE BEL WE SEW TRE 
b 3 T A : 
    
  
    
uted virtual city scene 
  
Figure.6 the user avatar in the distrib 
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